--- Truncate milliseconds
--- 2018-07-19 11:59:59.000
SELECT CONVERT(DATETIME, CONVERT(CHAR(19), '2018-07-19 11:59:59.999', 126))
--- Current Date Time with milliseconds truncated
SELECT CONVERT(DATETIME, CONVERT(CHAR(19), GETDATE(), 126)) SQL SERVER – Remove Milliseconds from Datetime in T-SQL
AX / Dynamics 365 For Finance and Operations blog 